Swift - Array to Dictionary - swift

Question

So, I have the following objects:
struct Person {
let name: String
let birthday: String
}
let Bob = Person(name: "Bob", birthday: "11.12.1987")
let Tim = Person(name: "Tim", birthday: "11.12.1987")
let John = Person(name: "John", birthday: "01.02.1957")
let Jerry = Person(name: "Jerry", birthday: "17.12.2001")
And the following array:
let people = [Bob, Tim, John, Jerry]
My goal is to generate a dictionary from this array, with "birthday" for the key and the "Person" object itself as the value: [String: [Person]]. If there are equal keys the person should be added and form an array as a key. So the result will be the following:
dictionary = ["11.12.1987": [Bob, Tim], "01.02.1957": John, "17.12.2001": Jerry]
What is the best way to achieve this?
Cheers!

Answer 1

You could use Dictionary(grouping:by:) method together with mapValues,
let result = Dictionary(grouping: people, by: \.birthday)
print(result)
Output is,
["01.02.1957": ["John"], "17.12.2001": ["Jerry"], "11.12.1987":
["Bob", "Tim"]]
This would yield you a Dictionary of type Dictionary<String, [Person]>.
From, your question it seems like you want a Person if there is only one Person and array when there are multiple people. You would loose type in that situation and your type would be something like this, Dictionary<String, Any>. You could make small bit of modification to the above code to do that.
let result = Dictionary(grouping: people, by: \.birthday)
.mapValues { people -> Any in
if people.count == 1 {
return people.first!
}
return people
}
print(result)
The output would be similar to what you want,
["01.02.1957": "John", "17.12.2001": "Jerry", "11.12.1987": ["Bob",
"Tim"]]

Answer 2

What about a loop through the dictionary checking if date exists. Otherwise create key with date and assign value.
If key already exists append person to the actual key value:
var dictionary = [String: [Person]]()
// Loop through all person objects in array
for person in people {
// Check if date already exists
if dictionary[person.birthday] != nil {
// If already exists, include new person in array
var array = dictionary[person.birthday]
array!.append(person)
}
// If date does not exists, add new key with date and person
else {
dictionary[person.birthday] = [person]
}
}